The GM 4L60, 4L60-E, 4L65-E and 4L70-E input drum assembly is known to crack and strip out splines where the input shaft is pressed into it (where the overrun piston rides). Sonnax offers a hardened steel sleeve that reinforces the input drum to prevent this failure. Sonnax input drum reinforcement kit 77733-51K includes a custom manufactured overrun piston designed for use only with a stamped steel forward piston, eliminating the need to use aluminum forward pistons.

• Custom overrun piston works with steel forward piston
• Chromoly steel sleeve design will not block clutch feed oil
• Universal design fits both early- and late-model units